Cargo containers need to be inspected at airports, seaports and other points of entry for transportation of contraband such as explosives, narcotics, currency, chemical and nuclear weapons, and for cargo-manifest verification. Detection of contraband with both high detection rates and low false alarm rates is a daunting task, as these materials often have similar physical characteristics as benign cargo. The percentage of cargo to be inspected is increasing and, because of the currently manually intensive nature of inspections, so is the number of operators. Therefore, there is a need to provide an automatic detection system to reduce the number of operators, or, at least, provide assistance tools that help operators improve their throughput by scrutinizing the cargo images more efficiently, thereby increasing detection and analysis speed.
Standard and advanced X-ray systems have difficulty detecting contraband in break-bulk cargo. This difficulty is exacerbated when inspecting larger and/or cluttered pallets and cargo containers.
Computed Tomography (CT)-based systems have been shown to be more suitable for the difficult task of detecting aviation-threat explosives in luggage and, more recently, in larger objects. However, existing high-energy CT systems for large objects are configured horizontally (horizontal gantry) with the object rotating around its axis. In one case, the source and detectors move vertically, and in the other case, the object moves vertically while the source and detectors are stationary. In both cases, the length of the scanned objects is limited by the system size and the configuration prevents scaling the system up to long objects such as large cargo containers and large skids.
U.S. Pat. No. 4,352,021, to the Regents of the University of California, describes “an x-ray transmission scanning system an electron beam scan tube for providing a plurality of adjacent movable x-ray sources comprising: an evacuated envelope having a longitudinal axis; an electron gun disposed axially at one end of the envelope projecting an electron beam along said axis; a focus coil spaced from said gun to receive and focus said beam; a plurality of adjacent longitudinally spaced curvilinear elongated targets disposed at the other end of said envelope to receive the electron beam and generate x-rays in response thereto; means for moving said focused electron beam along said targets and from one target to another; and a source collimator having an elongated slot disposed adjacent to each of said elongated targets to intercept said x-rays and provide an x-ray beam which fans outwardly from the received electron beam to form a fan shaped beam which rotates as the electron beam is moved along the corresponding target whereby to scan a plurality of adjacent longitudinally spaced sections at least one for each of said targets.”
In addition, U.S. Pat. No. 7,233,644, assigned to GE Homeland Protection, Inc. describes “[a] CT scanner for scanning an object by projecting x-ray fans from source points located along a source path to generate multiple views of the object, the CT scanner comprising a plurality of rastered x-ray tubes located in fixed positions in one or more scan planes, each rastered x-ray tube characterized by a raster path and capable of producing x-ray fans projected from different points along the raster path, wherein substantially all of the source points along the source path of the CT scanner are located on at least one of the raster paths of the x-ray tubes, wherein each x-ray tube is positioned such that the raster paths of adjacent x-ray tubes are substantially continuous.”
Large cargo containers require a relatively higher energy to be efficiently and effectively scanned for threat items. At the higher energy required, however, these approaches are not suitable for implementation due to cost, size, and complexity. Thus, the design and method of current detection systems limits the depth of information that can be obtained from scanned objects. Enhanced depth information typically requires a plurality of sources.
Therefore, there is a need for detection systems which are flexible and can scan objects of various sizes, while providing both depth information and images of high resolution that use a minimum amount of sources.
There is also a need for scanning systems that work on reduced cost, power consumption and machine size.